Method and apparatus for selectively removing metal from a metal part



Aug. 13, 1957 V w. P. 'LANGSFELD 2,

METHOD AND APPARATUS FOR SELECTIVELY REMOVING METAL FROM A METAL PART 2 Sheets-Sneet 1 F11 OOO. 25, 1954 INVENTOR. I? LHN SFEL Mum/'1 A TmRn/EY.

United States Patent METHOD AND APPARATUS FOR SELECTIVELY REMOVING METAL FROM A METAL PART Application October 25, 1954, Serial No. 464,301

8 Claims. (Cl. 41-43) This invention relates to the etching or removal of metal from the surface of a metal object or part, e. g. one comp-osed of iron, nickel, titanium, magnesium, zinc, aluminum or their alloys. More particularly the invention is concerned with novel apparatus and procedure for the controlled etching of a metal part or work piece to produce a desired contour or etch configuration thereon, and especially for the controlled simultaneous etching of a plurality of metal parts to produce substantially identical etch configurations on said parts. :It is known to etch acid soluble metals such as magnesium, zinc and their alloys with an acid solution such as aqueous nitri acid. It is also known to etch alkali solublemetals such as aluminum and its alloys with a solution having a solvent action on the aluminum or alloy surface, such as a hot aqueous alkali solution, e. g, one containing sodium hydroxide. One method of carrying out the etching process employing acids is to immerse the metal part to be etched in the etching bath, while another is to splash the solution contained in a bath against the work, the surface of which is to be etched or dissolved away. The prior art method for etching alkali soluble metals such as aluminum or its alloys is by immersion.

However, particularly where the purpose is to produce identically etched parts, I am aware of no prior art method or apparatus for the controlled selective etching of more than one part in order to successfully achieve this purpose.

One object of this invention is to devise novel apparatus and procedure for readily dissolving or removing metal in :a controllable manner from the surface of a metal work piece, e. g., composed of iron, nickel, aluminum, magnesium, titanium, zinc, and the like or their alloys, to impart a preselected contour or etch configuration to said work piece.

Another object is to provide apparatus and procedure for the controlled etching of a metal part.

Another object is to design novel apparatus and procedure particularly adapted for the uniform, controlled etching or removal of metal from the surface of a work piece particularly one composed of aluminum or its alloys.

A still further object is the provision of novel apparatus and procedure for controllably etching a plurality of metal parts or pieces to produce substantially identical etch patterns on such parts.

Yet another object is to provide apparatus and procedure for producing substantially identically tapered metal sheets, particularly of an aluminum base metal, by controlled etching.

1 Other objects and advantages will become apparent from the following description.

, -According to the invention, I can obtain parts having substantially identical shapes or contours by first securing or attaching two parts together in back to back relation. This can be accomplished by suitable means such as welding, riveting and the like. The abutting surfaces of the partssosecured to eachother are thus sea-ledto- 1 tached sheets can be immersed in the etch solution'at a ICE gether to substantially prevent ingress of etching solution between these surfaces. In this manner, only the opposite exposed surfaces of the parts can be etched or attacked by the etching solution to form the desired identical etch configurations thereon in the manner more fully described below, while the abutting surfaces of the parts are sealed and immune from attack by the etching solution. Hence this procedure automatically results in masking of the abutting or contacting surfaces of the attached parts without actually using the conventional forms of masking, e. g. a resist or wax composition, to inhibit attack of the metal surface by the etching solution.

The identical etch configurations so formed on the attached parts can have any desired shape, the formation of identically tapered parts constituting a preferred embodiment. After the attached parts have been etched to produce the desired identically shaped parts, or parts which are mirror images of each other, the parts are withdrawn from the etching solution and separated from each other in any suitable manner. Where riveting, for example, is employed to secure the parts together during etching, the outer periphery of the plates, including the rivets, can be sheared from the main body of the plates as described in greater detail below, to separate the parts.

The parts attached in back to back relation and to be identically shaped according to the invention are submerged in a bath containing a metal dissolving agent, i. e., an etching solution. Means are provided for then Withdrawing the attached work pieces from the bath at a preselected rate to thus controllably vary the time of immersion and amount of attack of the etching bath on different portions of each of the workpieces placed in the bath, corresponding opposite surfaces of the work pieces being simultaneously etched the same amount. When the attached work pieces are completely withdrawn from the bath, they will each be etched to a predetermined etch pattern, and the work pieces so treated according to the invention will have substantially the same etch pattern, shape or contour as result of such treatment.

Instead of withdrawing the work pieces at a preselected rate to obtain a predetermined etch pattern, the attached work pieces may be immersed in the etching solution at a preselected rate to obtain said predetermined etch pattern, and the work pieces then quickly withdrawn simultaneously from the etching bath after such pattern has been produced, in order to stop the etching action at this point.

Alternately, the parts secured back-to back according to the invention can be completely immersed in an etching bath and maintained immersed therein until the desired amount of etching takes place on the opposite exposed surfaces of the parts. The parts are then withdrawn from the solution and separated from each other to obtain parts having the same etch configuration.

The etch rate or amount of etching which takes place on the surface of a metal part in a given time is dependent on the concentration of the etching bath, the temperature thereof, and the time of immersion of the part. The etch rate for a particular bath can thus be predetermined, and by controlling the temperature and concentration of the etching bath, and the time of immersion of the part, the degree of etching at various portions of the exposed surface can be controlled to give a desired etch pattern. Thus, for example, if it is desired to produce identical tapered sheets, the portions of both sheets secured in back to back relation :according to the invention, and towhich the taper is to be applied can be immersed together in the etching bath, and the sheets withdrawn simultaneously vertically from the bath at a controlled uniform rate, depending on the etch rate of the sheets in that particular solution and the degree of taper desired. Or, the atcontrolled uniform rate to form the desired taper on the opposite exposed surfaces of the sheets, followed by rapid removal thereof from the solution. Hence, by securing a pair of sheets back to back according to the invention, two sheets of substantially identical taper can be produced. I

The metal parts tobe etched according to the'invention may be coated on corresponding selected portions of the surface thereof with a protective masking coating to inhibit or prevent attack by the etching agent while adjacent portions are available for such attack. in certain instances where it is desired to permit etching to at least some degree, of all surfaces of the work pieces submerged in the solution, a mask need not be used. The etched work pieces may be used in the decorative arts or in structures or machine parts.

Apparatus found particularly advantageous for carrying out the above procedure, i. 'e., for controlling the rate of withdrawal from an etching tank of a pair of work pieces secured back to back according to the invention to produce the desired identical etch patterns thereon includes a beam or lever, preferably reinforced along its length, pivotally supported on a pivot intermediate its ends. An elongated vertical support for one or more pairs of work pieces is suspended from the beam near one end thereof, the support having means at its lower end for securing the attached work pieces thereto. The connecting member between the vertical support and the beam, located at the upper end of such support is slidable along the beam for a limited distance. The connection and vertical support are disposed in a vertical guide for vertical movement only of said connection and its associated support, in response to pivotal motion of said beam. During the motion of the beam, the connection slides axially with respect to the beam while moving vertically in its guide. Means, e. g. in the form of a hydraulically controlled piston, is connected to the beam for pivoting same at a preselected rate to produce the desired rate of vertical movement of the support and immersion or withdrawal of the work pieces from the solution in order to obtain a predetermined etch pattern.

The invention will be more clearly understood by reference to the following description of a preferred embodiment taken in connection with the accompanying drawings wherein:

Fig. 1 is an elevational view, partly in section, of the invention device;

Fig. 2 is an enlarged section taken on line 2-2 of Fig. 1;

Fig. 2a is a section taken on line 2a-2a of Fig. 2;

Fig. 3 is an enlarged vertical section of the hydraulic cylinder and piston of the device of Fig. 1;

Fig. 4 is an enlarged section taken on line 4-4 of Fig. 1;

Fig. 5 is an enlarged elevational view of the mechanism for clamping a work piece, taken on line 5-5 of Fig. 1;

Fig. 6 is an elevation of a metal sheet to be etched, showing the mask applied thereto;

Fig. 7 is an end view of the sheet of Fig. 6;

Fig. 8 is an elevation of a pair of masked metal sheets united together back to back according to the invention.

Fig. 9 is a sectional view taken on line 9-9 of Fig. 8;

Fig. 10 is an enlarged sectional view taken on line 1010 of Fig. 8;

Fig. 11 is a sectional view of the assembly of Figs. 8 to 10, after etching of the sheets to form identical tapered sheets according to the invention;

Fig. 12 is a perspective elevational view of the tapered sheets shown in Fig. 11 after separation of the sheets from each other;

Fig. 13 shows a modification of etch configuration or contour of a pair of sheets obtainable according to the invention;

Fig. 14 shows another modification of etch configuration obtainable according to the invention;

Fig. 15 shows still another modification of etch configuration which may be produced according to the invention; and

Fig. 16 shows yet another modification of etch configuration obtainable by the invention process and apparatus.

Numeral 2% represents a tank in which the metal work pieces, parts or sheets of the invention are etched or sub- ;iectcd to the solvent action of a body of solution 21 maintained in the tank. Where the work pieces are composed of an acid soluble metal such as magnesium, iron, titanium, zinc or their alloys, the solvent solution can be of suitable acid composition such as aqueous nitric acid, aqueous hydrofluoric acid or mixtures thereof depending on the nature of the metal. According to the preferred embodiment of the invention for etching or removing metal from an aluminum or alluminum alloy material, which is alkali soluble, a hot aqueous solution is employed containing an alkali such as sodium or potassium hydroxide, trisodium phosphate, soda ash or the like, or mixtures thereof. Preferably a sodium hydroxide solution is used. Temperature of the solution in the etching tank is generally maintained in a range say from F. to about boiling during treatment. However, lower temperatures may also be used. The tank 20 has a series of coils 22 therein for circulation of steam or hot water to maintain the temperature of the solution in the tank.

Where an alkali soluble metal, e. g. aluminum, is being etched, the alkali concentrations employed in the bath range from 0.1 to 10 normal. Instead of NaOH I may use any of the other equivalent alkalis referred to above, adjusting the concentration to give the desired OH ion concentration. If desired, an acid etchant such hydrofluoric acid solution or solutions of salts such as ferric sulfate may be used for aluminum or aluminum alloys instead of alkali solutions.

Suspended over the top of tank 20 by means of bolts 23 passing into a supporting fixture 24 is a bracket 25 of essentially square configuration, having an upper horizontal member 26, a lower horizontal member 27, and vertical side arms 28 and 29. A beam or lever 33, normally inclined as seen in Fig. 1, is pivoted intermediate its ends on a pin 34 positioned on side arm 29, somewhat below the center thereof. The pin 34 is in the form of a threaded stud integrally positioned at one end of a T-shaped member 35 (see Fig. 4), the horizontal portion 36 of which receives the beam 33. A nut 37 threadably engages one end of the pivot pin 34 for adjustment there of, and a stud 34 is threadably received within portion 36, the end of stud 34' frictionally engaging beam 33 to prevent axial movement thereof with respect to member 35.

Suspended from a point near the upper end of beam 33 is an elongated vertical support 40 to the lower end of which, as will be described hereinafter, is attached one or more work pieces 41 which are treated in the etching solution in tank 20.

The vertical support 40 is suspended from beam 33 by means of a slidable connection or sleeve 42 which re ceives the beam and which is arranged from limited slidable movement therealong, as will be made clear below. The sleeve 42 is composed of half sections 43 and 44 (see Fig. 2a) clamped together at their adjacent ends by nut and bolt assemblies 45. Sleeve 42 is pivotally connected to the upper end of vertical support 40 by means of a pivot pin 46. Vertical support 40 slides in a vertical channel or guide 47, having a U-s'haped cross section and mounted on side arm 28 by meansof countersunk screws 48 passing through the channel and side arm 2821 the screws 48 having nuts 49 engaging their outer en s. 1

It is thus seen that when beam 33 is pivoted at 34' to rotate the beam counterclockwise or clockwise, connection or sleeve 42 will move'up or down in a vertical direction only in guide 47 While at the same time sliding inward or outward along beam 33 only a limited amount because of the restraint against lateral movement of the sleeve, due to its engagement within the guide 47. Thus, when beam 33 moves counterclockwise from its full line position shown in Fig. 1 to its horizontal dotted line position, sleeve 42 will have moved vertically downward along guide 47 and also laterally with respect to the hori- :zontal position 'of the beam, for example, from about .point50 to point 51. Of course, support 40 and the work pieces 41 suspended therefrom will also move only vertically up or down along guide 47 in response to vertical movement of sleeve 42 actuated by rotation of the beam 33.

Support 40 has attached 'to the lower end thereof a horizontal cross member 55. In the embodiment shown, three similar clamp assemblies 56 are supported on member'SS, two from. grooves 57 at opposite ends of member .55, and one from an eye 58 in the center of cross member 55. As seen in Fig. 5, each of clamp assemblies 56 includes a ring 62 extended downward to form a hook 63 :at its lower end, such hook in turn supporting a ring 64. To the lower end of ring 64 is connected a pair of links .65, the lower ends of which ;pivotally engage at 66 a pair of clamping levers v67 pivoted in scissors fashion on a pin 68 near their upper ends. Levers 67 have hooks 69 .at their outer ends for engaging the upper ends of Work pieces 41 to maintain samein vertically suspended position. Rods 70 are connected across levers 67, the tension on rods 70 being adjusted by means of turn- --buckle 71 for regulating the clamping force applied to levers 67. It will be understood that more or less than three pairs of plates 41 or plate assemblies maybe suspended from support 40 for immersion in the etching bath, and .that various types of clamping means other than clamp assemblies 56 may be employed for receiving the work pieces at-the lower end of support 40.

A reinforcing member 75 having .a pair of outwardly extending arms 76 and acentral depending support 77 is connected at its lower ends to beam 33 intermediate pivot pin 34 and sleeve 42. Connected to the lower end of "beam 33 beyond pivot pin 34 is a counterweight 78 adjustable along beam 33 by means of the set screw 79.

Beam 33 is actuated for pivotal motion thereof by 'a-piston '83 sliding in a cylinder 84. The cylinder 84 is pivotally mounted by means of pivot pin 85 on an extension 86 of the upper horizontal member 26 of bracket 25,

and the external lower end of the piston arm 87 is-connected by pivot pin 88 to beam 33 between its pivot point 34 and the counterweight 78. A packing gland 89 (see Fig. 3) threadably engaging a depending flange 90 at the bottom of the cylinder 84 receives piston arm 87, for slid- :able movement thereof, and maintains packing 91 within flange 90 in proper position to prevent leakage of fluid inline 98 into the lower chamber 99 of cylinder 84, while valve 100 in outlet '100' is closed, will force piston 83 upward, causing beam 33 to pivot counterclockwise to :lower support 40 and the work pieces thereon. When cfluid is being introduced into the upper chamber 96 to lower piston 83, fluid in lower chamber 99 isbled through line'100' and valve 100, and when fluid is introduced into Ithe lowerchamber 99 to raise piston 83, fluid in upper chamber 96 is bled through line 97' and valve 97.

Referring now particularly toFigs. 6 to 12, according pattern 111.

to the invention for producing metal parts or.sheets having the same contour or etch configuration, for example, identically tapered sheets, the sheets 41 of stock are cut oversize, for example, about /z.about the entire outer periphery. A masking coat 185 is then applied to this peripheral area on one side of each sheet, forming in effect a frame of coating about the sheets to .be treated. Two such sheets are then placed back to back in contact with each other, .the mask on each of the plates'facing outward. The sheets are then riveted together as seen in Fig. 9, by means of rivets 106 positioned in the outer peripheral area of the plates covered by mask .105, as shown in Fig. 8. A masking coat .107 is then applied about all four outer edges of both sheets 41 and also between .the sheets along their mating peripheral edges to form a gasket 108 to prevent introduction of etching fluid between the plates. The rivets 106 may be made of a metal which is not attached by the etching solution, .such as soft steel or other metal Where the sheets 41 to be etched according to the invention are aluminum or an aluminum alloy, and where the etching bath is caustic alkali. For further protection, the rivets may also be coated with a coat 109 of masking material, as seen in Fig. 10. If desired, means other than riveting, as for example clamps, may be used to hold the plates 41 together in back to back relation.

.Any number of the assemblies shown in Fig. 10, for example three such assemblies as seen in Fig. 1, are then mounted at the lower end of the vertical support 40 of.Fig. 1, by means of the clamp assemblies 56 shown'in Fig. 5, and the sheets 41 are lowered into the etching solution 21 by actuation of piston 83 upward to rotate beam 33 clockwise, until such sheets are entirely immersed in the solution, as shown in dotted lines in Fig. l. Piston 83 is then actuated to move slowly downward at a preselected uniform rate, causing beam 33 to rotate clockwise at a uniform rate, which in turn permits the sheets 41 to be simultaneously slowly and uniformly withdrawn from the etching solution 21. Since the sheets are gradually removed from the etching bath in this manner, the upper areas 110 of sheets 41 not covered by masks 105 will be etched the least, those areas below and adjacent thereto will be etched more, and so on, so

.that the lowermost portions 110' of the uncovered areas of sheets 41 will be etched most, inasmuch as the latter portions are the last to be removed from the solution.

.By this means, a gradual downward taper 111 is formed trolled rate of withdrawal of sheets 41 from the solution as described immediately above, piston 83 can be actuated to move slowly upward at a preselected uniform rate, to cause beam 33 to rotate counterclockwise and permitting sheets 41 to be immersed simultaneously and at a uniform cont-rolled rate to produce the tapered etch Following complete immersion of sheets 41 and (formation of the taper 111, piston 83 is then actuated downward at a rate permitting beam 33 to rotate clockwise for rapid withdrawal of sheets 41 from the solution. It is seen that this mode of procedure involving controlled rateof immersion also results in a longer period of attack of the lower portion of the sheets 41 by the solution than the upper portion of such sheets, forming the downward taper 111.

'Since the two sheets 41 in each of the assemblies as shown in Fig. 10 are immersed in or withdrawn from the etch bath 21 simultaneously and at identical rates the degree of etching taking place at corresponding points at the same height will be identical. For example, the amount .of etching at points 111' and 112 will be the same, and that at points 113 and 114 will be the same. Thus, the two sheets 41 in each of the assemblies as represented in Fig. 11 will have identical etch contours or tapers.

When the treated sheets have been completely removed from the etching solution, as shown in Fig. 1, the sheet assemblies are removed from clamping-levers 67, and the pairs of tapered sheets in such assemblies are separated by shearing ofif the peripheral portions of the sheets covered by masks 105, 107, 103 and 102, and containing rivets 106. Thus, for example, the portions of tapered sheets 41 above line x-x and below line yy in Fig. 11, as well as the corresponding end portions of these sheets are removed, leaving the finished identically tapered plates 41 shown in Fig. 12.

From the foregoing, it is seen that two identical parts, that is, having identical contours, can be produced according to the invention, or a right hand and left hand part can be produced simultaneously. Further, the original finish and surface of one side of each part can be preserved by utilizing that side as the backing mask, that is, by placing that side in back to back abutting relation with a side of the companion part to be similarly contoured according to the invention.

.Also, parts having identical shapes or contours other than tapered can be produced by my invention. Thus, in Fig. 13 two identical parts 120 each having a rounded outer surface 121 can be formed, e. g. by proper control of the rate of withdrawal of the part from the etching solution. In Fig. 14 is shown another modification consisting of two identical parts 125 each having an upper tapered portion 126, an intermediate non-tapered portion 127 and a lower tapered portion 128. The intermediate straight portion 127 can be formed, for example, by

quickly Withdrawing the part from the solution a distance equal to that between the upper and lower tapered portions 126 and 128. With respect to parts 120 and 125, the back surfaces 129 and 130, respectively, thereof are masked by securing the parts together in abutting back to back relation prior to etching according to the invention, to prevent attack of these surfaces by the etching bath. In Fig. 15 is shown two identical parts 131 each having its opposite exposed surface 132 identically contoured according to the invention. In Fig. 16 is shown yet another modification wherein parts 133 have their opposite sides 134 identically shaped in the form of a half oval by means of the back to back etching principles of the invention. The respective pairs of parts 131 and 133 are secured in back to back relation along their abutting surfaces 135 and 136 respectively prior to etching.

It is understood that in order to produce parts having the same final three dimensional shape as a result of the etching procedure according to the invention without further operation on the etched portions, the geometrical shape and dimensions of the original parts whose shape is to be altered by the etching solution should preferably be substantially the same. However, where it is desired to etch the surface of the parts to produce substantially identicaletch patterns on such surface portions, it is not necessary that the original parts have the same geometry in all dimensions. In this case the two parts may be properly masked so as to leave exposed surface portions of substantially identical shape and area, the parts secured back to back to leave said opposite exposed surface portions of the parts available for attack by the etching solution, and the parts subjected to simultaneous treatment ,by the etching solution according to the invention, for example, by controlled rate of immersion in or Withdrawal from the solution, or by complete immersion of the parts for the desired period.

It is not necessary to maintain concentration and temperature of the etching bath constant, since regardless of these parameters, the two parts secured back to back according to the invention will always be subjected to the same etching conditions and hence will be etched to the same degree. However, where it is desired to obtain specific predetermined identical shapes such as identically tapered parts, for example, by controlled withdrawal from or immersion in the etching bath, it is preferred to control the etch bath temperature and concentration, that is, so as to maintain these parameters substantially constant.

In addition to the formation of parts having identical etch patterns or'shapes, the invention may be applied where it is desired to etch down the surfaces of two parts the same amount regardless of the geometrical shape of such surfaces. Here, the parts are connected together in back to back relation, leaving the surfaces to be etched exposed. The parts are then immersed in the solution and the etching treatment continued for a time sufiicient to etch the desired thickness of metal from the exposed surfaces of both parts. The parts are then withdrawn from the solution and separated from each other.

Of course it will be understood that the apparatus described herein for supporting the work pieces in the etching solution in back to back relation according to the invention, should be constructed of materials which are substantially inert to attack by the etchant solutions employed, and those skilled in this art will know how to select such materials.

While I have described a particular embodiment of my invention for the purpose of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.

I claim:

1. A method of substantially equally and correspondingly etching metal parts with an etching solution, which comprises securing a pair of said parts together in back to back relation so as to mask the adjacent back surfaces of said parts, said parts having respective opposite surface portions exposed for attack by said etching solution, simultaneously immersing said parts in an etching solution with the plane of said backs substantially normal to the surface of said solution, said parts being introduced into and withdrawn from the solution at a rate selected to vary the period of immersion and amount of attack of the etching solution on different sections of the exposed surface portions of each of said parts, corresponding opposite sections of the exposed surface portions of said parts, with reference to the surface of the solution, being thereby etched substantially the same amount.

2. A method as set forth in claim 1, wherein the selected variation in the period of immersion is effected during the withdrawal of said parts from said solution.

3. A method as set forth in claim 1, wherein the selected variation in the period of immersion is effected during the introduction of said parts into said solution.

4. A device for controlling the rate of movement of a work piece into and out of a body of liquid, which comprises a beam, said beam being pivotally supported intermediate its ends, a support for said work piece slidably suspended adjacent one end on said beam, means for guiding said support for vertical movement in response to pivotal motion of said beam, and means connected to said beam for pivoting same at a preselected rate to produce a corresponding vertical movement along said guiding means, of said support for said work piece.

5. A device for controlling the rate of movement of a work piece into and out of a body of liquid, which comprises a beam, said beam being pivotally supported 1 intermediate its ends, an elongated support for said work piece slidably mounted on said beam adjacent one end thereof, means for guiding said support for vertical movement only, in response to pivotal motion of said beam, and means connected to said beam for pivoting same at a preselected rate to produce a corresponding vertical movement along said guiding means of said support for said work piece.

6. A device for controlling the rate of movement of a work piece into and out of a body of liquid, which comprises a beam, said beam being supported for pivotal movement on a pivot intermediate its ends, an elongated vertical support for said work piece suspended from said beam near one end thereof, a connection between said support and said beam, said connection being slidable for a limited distance on said beam, a guide for vertical movement only of said connection and said support in response to pivotal motion of said beam, and means connected to said beam for pivoting same at a preselected rate to produce a corresponding vertical movement along said guide of said support for said work piece.

7. A device for controlling the rate of movement of a work piece into and out of a body of liquid, which comprises a beam, said'beam being supported for pivotal movement on a pivot intermediate its ends, an elongated vertical support for said work piece suspended from said beam near one end thereof, means at the lower end of said support for securing a work piece thereto, a connection between said support and said beam, said connection being located at the upper end of said support and being slidable for a limited distance on said beam, a guide for vertical movement only of said connection and said support, in response to pivotal motion of said beam, and hydraulic means connected to said beam for pivoting same at a preselected rate to produce a corresponding vertical movement along said guide of said support for said work piece.

8. A device for controlling the rate of movement of a work piece into and out of a body of liquid, which comprises a beam, said beam being supported for pivotal movement on a pivot intermediate its ends, an elongated vertical support for said work piece suspended from said beam near one end thereof, means at the lower end of said support for securing a work piece thereto, a connection between said support and said beam, reinforcing means on said beam between said connection and said pivot, a counterweight on said beam on the opposite side of said pivot, said connection being located at the upper end of said support and being slidable for a limited distance on said beam, a guide for vertical movement only of said connection and said support, in response to pivotal motion of said beam, and hydraulic means connected to said beam for pivoting same at a preselected rate to produce a corresponding vertical movement along said guide of said support for said work piece.

References Cited in the file of this patent UNITED STATES PATENTS 196,467 Macbrair Oct. 23, 1877 493,027 Hoggson Mar. 7, 1893 2,157,845 Bernarde May 9, 1939 FOREIGN PATENTS 104,510 Great Britain Aug. 2, 1917 

1. A METHOD OF SUBSTANTIALLY EQUALLY AND CORRESPONDINGLY ETCHING METAL PARTS WITH AN ETCHING SOLUTION, WHICH COMPRISES SECURING A PAIR OF SAID PARTS TOGETHER IN BACK TO BACK RELATION SO AS TO MASK THE ADJACENT BACK SURFACES OF SAID PARTS, SAID PARTS HAVING RESPECTIVE OPPOSITE SURFACE PORTIONS EXPOSED FOR ATTACK BY SAID ETCHING SOLUTION, SIMULTANEOUSLY IMMERSING SAID PARTS IN AN ETCHING SOLUTION WITH THE PLANE OF SAID BACKS SUBSTANTIALLY NORMAL TO THE SURFACE OF SAID SOLUTION, SAID PARTS BEING INTRODUCED INTO AND WITHDRAWN FROM THE SOLUTION AT A RATE SELECTED TO VARYING THE PERIOD OF IMMERSION AND AMOUNT OF ATTACK OF THE ETCHING SOLUTION ON DIFFERENT SECTIONS OF THE EXPOSED SURFACE PORTIONS OF EACH OF SAID PARTS, CORRESPONDING OPPOSITE SECTIONS OF THE EXPOSED SURFACE PORTIONS OF SAID PARTS, WITH REFERENCE TO THE SURFACE OF THE SOLUTION, BEING THEREBY ETCHED SUBSTANTIALLY THE SAME AMOUNT. 